From Ocean to Market: Technical Applications of Fish Protein Hydrolysates in Human Functional Food, Pet Wellness, Aquaculture and Agricultural Bio-Stimulant Product Sectors

Abstract

Sustainability in food production is a pressing priority due to environmental and political crises, the need for long-term food security, and feeding the populace. Food producers need to increasingly adopt sustainable practices to reduce negative environmental impacts and food waste. The ocean is a source for sustainable food systems; deforestation, water scarcity, and greenhouse gas emissions burden traditional, terrestrial resources. Our oceans contain the largest unexploited resource in the world in the form of mesopelagic fish species, with an estimated biomass of 10 billion metric tons. This resource is largely untapped due in part to the difficulties in harvesting these species. To ensure sustainability of this resource, management of fish stocks and fish processing practices must be optimised. Generation of fish protein hydrolysates from by-catch/underutilised species creates high-value, functional ingredients while also reducing waste. Marine hydrolysates offer a renewable source of nutrition and align with the principles of the circular economy, where waste is minimised and resources are reused efficiently. Ocean-derived solutions demand fewer inputs, generate less pollution, and have a smaller carbon footprint compared to traditional agriculture. This review collates clearly and succinctly the current and potential uses of FPHs for different market sectors and highlights the advantages of their use in terms of the scientifically validated health benefits for humans and animals and fish, and the protection and crop yield benefits that are documented to date from scientific studies.

1. Introduction

Protein hydrolysates are manufactured primarily through enzymatic or chemical hydrolysis using proteolytic enzymes. While techniques such as high-pressure processing (HPP), ultrasound, and heat-treatment are used to aid in protein unfolding and enhance the exposure of specific amino acid residues, thereby improving enzyme accessibility and hydrolysis efficiency [1,2,3]. Protein hydrolysates are known to exhibit a wide spectrum of bioactivities—ranging from antimicrobial, anti-inflammatory, and antioxidant effects to anti-hypertensive, anti-diabetic, appetite-regulating, and weight management benefits. However, these functional properties are intrinsically linked to the release of specific bioactive peptides and are highly influenced by the amino acid composition and the positional arrangement of these residues within the peptide chains [4,5]. Bioactive peptides are defined as short chains of amino acids—typically comprising two to thirty residues—that, once liberated from their parent protein, can exert physiological effects and confer health benefits [6]. These peptides are incorporated into foods, nutraceuticals, and pharmaceutical formulations, and can be delivered through various routes including oral, nasal, and rectal administration, or applied topically, as in the case of cosmetics and dermatological treatments [7].

Fish protein hydrolysate (FPH) generation has gained popularity as a strategy to add value to fish processing co-products of primary production and to reduce food waste and develop new ingredients and new markets, adding value to the harvested fish resource or fish processed from aquaculture production. The health benefits of FPHs are well documented and several FPH products are sold globally for human health benefits [8,9]. However, regulations with regard to making health claims in Europe and elsewhere including the USA, Japan, and China are strict and require significant financial and scientific investments to enable products to be placed on the market [9]. Development of functional foods/nutraceuticals is similar in terms of the strategy required for the development of pharmaceutical bioactives and requires careful characterisation of bioactives, pre-clinical, and clinical trials. Different markets can be developed for FPHs, intended for the human market, during characterisation of the hydrolysates [10]. Herein, we detail the use of FPHs and bioactive peptide products in pet care ingredients and palatants as ingredients for use in aquaculture and as biostimulants agents in agriculture. Existing details of products in these sectors are collated and studies concerning the use of FPHs in pet feed and aquaculture for animal health benefit are described. Work concerning the regulations of FPHs as human, pet, and aquaculture feed ingredients and as biostimulants are cited within.

2. FPHs for Human Functional Benefits

Functional foods impart health benefits to the consumer that go beyond basic, human nutrition [11]. They provide effects such as anti-hypertension, anti-inflammatory, and anti-microbial actions, bone and skin health benefits, inhibition of enzymes that play roles in diseases associated with metabolic syndrome like type-2 diabetes (T2D), obesity and others [12,13,14,15,16]. FPHs, rich in bioactive peptides generated through enzymatic protein degradation, have been shown to modulate key enzymes involved in maintaining human health. These include alpha-amylase and dipeptidyl peptidase-IV, which contribute to type 2 diabetes (T2D) management and satiety regulation, as well as angiotensin-converting enzymes (ACE-1 and ACE-2) and renin, whose inhibition is associated with blood pressure reduction [17]. Hydrolysates find applications as human functional foods in different food categories, including Speciality Foods that encompass different product formats including snack products, frozen refrigerated goods, cheese, and plant-based products, breads/baked goods, entrées, coffee, chocolate/confectionary ingredients, desserts, and water. They are also found within the health and wellness category of food products, where they are promoted for their positive effects on inflammation, heart health, mood, anxiety prevention, and the promotion of sleep, gut health benefits, as well as several other health impacts [18]. A range of FPHs, including those derived from pelagic species, are commercially available and marketed with various health-related claims, as summarised in Table 1. These products are predominantly sold as ingredients for use in functional foods and dietary supplements. However, only a limited number have secured approval from the European Food Safety Authority (EFSA) for novel food status or authorised health claims within the European Union (EU) [19]. An exception to this is the thermolysin Bonito fish hydrolysate with active ingredient LKPNM. This hydrolysate has antihypertensive activities and has held Foods of Specified Health Use (FOSHU) status since 1997 in Japan [20]. This product does not have a cause and effect EFSA health claim for antihypertensive activity. EFSA found that a cause-and-effect relationship was not possible for the maintenance of normal blood pressure claims due to the active ingredient LKPNM, but the Bonito hydrolysate did receive Novel Food Status from EFSA [21]. There is a need to carry out human dietary intervention and clinical trials for FPHs if health claims are sought. This is just one, largely economic barrier towards the use of FPHs on a wide-scale basis in preventative medicine.

2.1. FPH with Anti-Inflammatory Activities

FPH may be rich in anti-inflammatory peptides with the potential to inhibit/impact various enzymes involved in the process of inflammation. These peptides are usually positively charged, containing amino acids like lysine, arginine and histidine, short peptides (usually 2–10 amino acids in length) with low molecular weights, and contain hydrophobic amino acid residues including Alanine, Valine, Proline, Isoleucine, Leucine, and others. Molecular weight cut off filtration may be used to generate extracts rich in these peptides (usually <3000 Da in size) [22]. Anti-inflammatory activity may be due to the amino acid composition or the folding of the peptide and sidechain interactions with the targets. Targets include cyclooxygenase (COX-1, COX-2) enzymes IL-6, IL-8 and TNF-α [23]. Examples of fish derived anti-inflammatory hydrolysates containing characterised peptides include a blue mussel hydrolysate >5 kDa in size where the anti-inflammatory activity is likely due to the secondary and tertiary structure of larger peptides found in the hydrolysate [24]. An Alcalase hydrolysate of the Green-lipped mussel containing the peptide sequence EGLLGDVG could downregulate COX-2 protein expression and iNOS in RAW 264.7 mice macrophage cells [25]. The peptides SNKGGGRPN, PGVATAPTH, LLGLGLPPA derived using papain applied to salmon bones also was found to inhibit COX-2, NO, IL-6, iNOS, and TNF-α mRNA in RAW 264.7 mice macrophage cells [26]. Other examples of FPH with anti-inflammatory activity are available in the excellent review of Kemp and colleagues [24]. Antihypertensive hydrolysates were also developed from Blue whiting and mackerel co-products of processing recently for use in companion animals [27].

2.2. FPH with Anti-Hypertensive Activities

Examples of FPH with anti-hypertensive activities that are commercially available include Valytron^® with the active, bioactive peptide VY derived from Sardine muscle as well as Vasotensin Peptide 90 derived from Katsuwonus pelamis containing the active peptide LPK and LKPNM (Table 1) [28,29]. Bioinformatics tools are used to predict in vitro ACE-1 and Renin inhibitory effects. Indeed, Abdelhedi and colleagues demonstrated that ACE-1 inhibitory peptides are usually derived from actin and collagen (alpha-1 and alpha-2) proteins and enzymes including papain and Alcalase [30]. ACE inhibition is either competitive or non-competitive inhibition of the ACE-1 enzyme. Competitive enzyme involves interaction of the inhibitor with the active enzyme sites to prevent substrate binding and non-competitive inhibition involves binding of the molecule to the free enzyme and the enzyme–substrate complex [31]. Naik, Mora, and Hayes identified several ACE-1 inhibitory peptides from hydrolysates generated from Blue mussels [32]. Peptides identified as ACE-1 inhibitory in these hydrolysates include those with sequences FNAEKGFGF, KPEAPKVP, and SSDVPGV [32]. Renin inhibitory FPH were developed from cod previously and the most active peptides were assessed for their ability to reduce systolic blood pressure (SBP) in spontaneously hypertensive rats (SHRs) [33]. ACE-1 and Renin inhibition IC₅₀ values of 0.13 mg/mL and 0.16 mg/mL, respectively, were reported [33].

2.3. FPH with Anti-Diabetes Type 2 (T2D) and Satiety Activities

FPH may contain peptides that can affect the progression or prevent T2D. Peptides from FPH can stimulate glucagon-like peptide-1 (GLP-1) secretions and enhance insulin release from pancreatic cells and may also inhibit enzymes like dipeptidyl peptidase-IV activity (DPP-IV), resulting in an increase in glucose uptake and tolerance, a reduction in blood glucose concentration, and the up-regulation of GLUT4 [34]. Zhou and colleagues [35] recently collated a review on fish and milk derived peptides from hydrolysates and their impact on T2D development [35]. A review of the literature concerning FPH and in vivo studies came to the conclusion that even though there is methodological variation between several studies performed to date, there is significant potential for the application of FPH to control hyperglycaemia and weight [35]. A study by Cudennec and colleagues demonstrated both in vitro and in vivo evidence for a satiating effect of FPH obtained from blue whiting (Micromesistius poutassou) muscle [36]. Several in vivo studies with FPH looking at the anti-hyperglycaemic effect of FPH have shown a reduction in blood glucose with doses of FPH as low as 50 mg kg⁻¹ bodyweight [37].

Furthermore, all in vivo studies investigating the satiating effect of FPH have shown a decrease in bodyweight or a reduction in weight gain [38]. Antidiabetic peptides mainly inhibit dipeptidyl peptidase-IV (DPP-IV) activity. Inhibitors of DPP-IV can cleave incretins like glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GDP). Li-Chan and colleagues generated the peptide GPAE from salmon gelatine previously and this peptide was shown to have considerable inhibitory effects on DPP-IV [39]. DPP-IV inhibitory peptides were also identified from discarded Sardine pilchardus protein previously [39,40].

2.4. FPH with Bone and Skin Health Implications

FPHs have emerged as powerful multifunctional ingredients for skin health, with growing evidence supporting their role in combating photoaging and pigmentation disorders [41,42]. Sourced from a variety of marine species, FPHs are rich in bioactive peptides that exert a wide range of beneficial effects, including antioxidant, anti-inflammatory, anti-apoptotic, and anti-melanogenic actions. These peptides not only help preserve extracellular matrix integrity and enhance skin hydration but also protect against UV-induced oxidative stress and DNA damage, making them ideal candidates for functional foods, nutraceuticals, and cosmeceuticals [43].

Recent studies have illuminated the molecular mechanisms behind these effects. Chen et al. [44] demonstrated that gelatine peptides from Pacific cod skin inhibited MMP-1, MMP-3, and MMP-9 by suppressing the MAPK pathway, thereby preserving collagen and enhancing dermal structure in UV-exposed skin. Similarly, Li et al. [45] found that silver carp scale-derived peptides (SCPs1) inhibited melanogenesis in B16 melanoma cells via downregulation of the cAMP-CREB-MITF axis. These peptides also exhibited strong antioxidant activity by reducing reactive oxygen species (ROS) and boosting intracellular glutathione levels, positioning them as dual-function agents for both skin brightening and oxidative protection.

Furthering this line of research, Losageanu et al. [46] investigated peptides from silver carp bones (FBBPs), reporting cytoprotective effects in UVB-irradiated skin cells, suppression of TNF-α in inflamed macrophages, and significant reductions in melanin production and tyrosinase activity. Complementing these findings, Kong et al. [47] identified three peptides—TCP3, TCP6, and TCP9—from skipjack tuna, which protected keratinocytes from UVB damage by stabilising mitochondrial membrane potential and regulating apoptosis-related markers through activation of the Nrf2–Keap1 pathway.

2.5. FPH with Antioxidant and Antimicrobial Activities

Oxidative stress, a key contributor to the degradation of essential biomolecules in both biological systems and food matrices, is closely linked to cellular impairment, tissue damage, and the decline of food quality. Antioxidants serve as critical defenders against this process by neutralising free radicals and interrupting oxidative chain reactions [48]. In recent years, marine-derived proteins have gained significant attention as a rich source of natural antioxidant peptides, owing to their promising bioactivity and diverse structural profiles [49]. A growing body of research has focused on the enzymatic hydrolysis of proteins from various fish species to isolate and characterise peptides with strong antioxidative potential [50,51,52,53]. These peptides, typically under 6000 Da in molecular weight, display activity influenced by several key factors, including peptide length, amino acid sequence, hydrophobicity, and overall composition [54].

Halim et al. [50], in their review of FPHs, noted that short-chain peptides composed of 2 to 10 amino acid residues tend to exhibit superior antioxidant efficacy. This heightened activity is largely attributed to the presence of specific amino acids known for their redox potential. Hasani et al. [51], further supported this observation in a study utilising Indian mackerel waste hydrolysed with Alcalase and Flavourzyme, revealing that residues such as valine, leucine, proline, histidine, and particularly tyrosine play pivotal roles. Tyrosine, for instance, acts as an effective electron donor, helping to stabilise reactive species and prevent oxidative damage.

Peptides exert their antioxidant effects through various mechanisms. Firstly, they can donate hydrogen atoms or electrons to free radicals, effectively neutralising and stabilising these reactive species and thereby preventing oxidative damage to biological molecules [50,55]. Secondly, peptides possess the ability to chelate transition metal ions such as iron and copper, which are key catalysts in the generation of reactive oxygen species; by binding these metals, peptides inhibit the redox reactions that fuel oxidative stress [56,57]. A third mechanism involves the direct interaction of peptides with reactive oxygen species, through which they interrupt the lipid peroxidation chain reaction and halt the propagation of oxidative damage across cellular membranes or food lipids [58]. Lastly, peptides may function as physical barriers by forming protective layers around lipid droplets, thereby preventing the penetration of pro-oxidative initiators and safeguarding lipid molecules from degradation [59].

Bi and colleagues [60] identified three potent antimicrobial peptides from the enzymatic breakdown of Turbot viscera. These peptides, generally comprising between 1 and 50 amino acids, had molecular weights under 10 kDa. Structurally, they exhibited amphipathic properties, were notably enriched in cysteine, and carried a net cationic charge in their active conformation—features that enabled them to effectively target and disrupt bacterial cell structures.

In their study, Pezeshk and colleagues [52] enzymatically hydrolysed the viscera of yellowfin tuna (Thunnus albacares) and fractionated the hydrolysate into four distinct molecular weight fractions via membrane ultrafiltration (<3 kDa, 3–10 kDa, 10–30 kDa, and >30 kDa). They evaluated the antioxidant and antibacterial activities of both the unfractionated hydrolysate and its individual fractions. The findings revealed that the smallest molecular weight fraction (<3 kDa) exhibited the most potent antibacterial effects, significantly inhibiting both Gram-positive bacteria and Gram-negative strains. These results underscore the exceptional structural and functional traits of marine-derived antimicrobial peptides, which tend to show diverse structural motifs, broad-spectrum activity, limited sedimentation, and high bacterial target specificity.

Perez Espitia et al. [61] proposed that antimicrobial peptides exert their effects by first attaching to the pathogen cytoplasmic membrane. This initial interaction is followed by the formation of pores within the membrane structure. These pores compromise the membrane’s structural and functional integrity, which in turn interferes with vital processes such as cellular respiration and the maintenance of electrochemical gradients. As a result, uncontrolled movement of water and ions into the cell occurs, causing cellular swelling and, ultimately, lysis.

Two primary mechanisms have been proposed to describe how antimicrobial peptides form pores in bacterial membranes: the carpet model and the barrel-stave model [61]. The carpet model involves peptides spreading across the membrane surface like a “carpet”. Once a critical concentration is reached, these peptides destabilise the membrane through a combination of hydrophilic and hydrophobic interactions. This destabilisation leads to the formation of transient pores or micelle-like structures, disrupting membrane integrity and resulting in its complete disintegration. Conversely, in the barrel-stave model, peptides adopt amphipathic alpha-helical structures that insert themselves perpendicularly into the lipid bilayer. Their hydrophobic regions interact with the lipid tails of the membrane, while the hydrophilic sides face the interior of the formed pore. As more peptides accumulate, these channels enlarge, leading to membrane permeabilization, leakage of intracellular components, and eventual cell death.

Da Rocha [62] highlighted that the antimicrobial effectiveness of protein hydrolysates derived from Umbrina canosai is influenced by a range of interrelated factors. These include the peptide’s hydrophobicity, net charge, amino acid profile, size, and secondary structure, as well as environmental parameters such as pH, temperature, and ionic strength. Additionally, the source of the peptide, its concentration, and the presence of surfactants play significant roles. Importantly, the structural characteristics of the bacterial membrane also contribute to determining how effectively these peptides can exert their antimicrobial action.

Table 1. Fish protein hydrolysate (FPH) products with associated health benefits.

Product Name	Manufacturer	Fish Source and Active Ingredient	Health Benefit Claimed	References
Jellice (hydrolysate) found in CollametaTM	Jellice Pioneer Europe PV, (7821 BG, Emmen, The Netherlands); supplied into product CollaMeta produced by Glanbia Nutritionals Ltd. (Global)	Skin from Tilapia and Pangasius sp./Collagen tripeptide	Skin health, possible prevention of arthritis in humans	[63]
Collagen HMTM	Copalis, France (Le Portel, Hauts, France)	Different fish sources including white fish species and salmon/Collagen HMTM polypeptides mean molecular weight is 3600 Da, making it soluble in aqueous phase and fully digestible	Skin and joint health	[64]
NutripeptinTM	Copalis, France (Le Portel, Hauts, France)	Bioactive marine peptide	Reduces the glycaemic index of foods and thus helps to reduce fat storage in weight-control formulas	[65]
ProtizenTM	Copalis, France (Le Portel, Hauts, France)	Pollock and coalfish digest produced by enzymatic hydrolysis/anti-stress peptide that promotes well-being, found in Serenlider product—possess anxiolytic properties and is considered as beneficial for mental health/stress	Anti-stress, mood food, promotes restful sleep	[66]
Molval®	Dielen Laboratoire, France (Cherbourg-en-Cotentin, Normandy, France)	Extracted from cod and mackerel/Gabolysat PC60.	Beneficial effects on dyslipidaemia and cardiovascular risk, contains omega-3 fatty acids and Gabolysat PC60/anti-stress effects	[67]
Curcumega®	Dielen Laboratoire, France (Cherbourg-en-Cotentin, Normandy, France)	Fish oil rich in omega-3 fatty acids combined with turmeric	Nutritional impact and antioxidative effects	[67]
Seagest®	Trimedica, USA (Santa Monica, CA, USA)	Deep ocean within fish species		none found
PeptACE®	Natural factors, USA (14224 167TH Ave SE Monroe, WA, USA)	Bonito fish hydrolysate/nine small peptides derived from Bonito fish	Maintains normal blood pressure	[68]
Stabilium® 200	Nutricology, Canada (Salt Lake City, UT, USA)	Derived hydrolysate from Molva dypterygia	Improves resilience to stress, may reduce fatigue and supports normal psychological functions, such as memory, concentration, and cognitive abilities	[69]
Amizate®	Zymtech Production AS, Norway (Oppland, Lesja)	Enzymatic process extracts amino acids, short peptides, and micronutrients from Atlantic salmon (Salmo salar)	Excellent nutritive value; mood improving agent	[70]
WhiteCal®	BioMarine Ingredients Ireland (BII), Ltd. (Ballybay, Monaghan, Ireland)	Blue whiting fish/WhiteCal is a marine mineral complex, naturally rich in collagen peptides and high in calcium, phosphorus, and magnesium. It can be easily used in a wide range of human nutrition applications	Growth and repair of the body and maintenance of good health, bone, and joint health.	[71]
ProAtlantic®	BioMarine Ingredients Ireland (BII), Ltd. (Ballybay, Monaghan, Ireland)	Premium grade hydrolysed Fish Protein Isolates (FPI) containing 95% protein and 0.5% fat for human products	Glycaemic control, diabetes prevention, satiety	[72]

Table 1. Fish protein hydrolysate (FPH) products with associated health benefits.

Product Name	Manufacturer	Fish Source and Active Ingredient	Health Benefit Claimed	References
Jellice (hydrolysate) found in CollametaTM	Jellice Pioneer Europe PV, (7821 BG, Emmen, The Netherlands); supplied into product CollaMeta produced by Glanbia Nutritionals Ltd. (Global)	Skin from Tilapia and Pangasius sp./Collagen tripeptide	Skin health, possible prevention of arthritis in humans	[63]
Collagen HMTM	Copalis, France (Le Portel, Hauts, France)	Different fish sources including white fish species and salmon/Collagen HMTM polypeptides mean molecular weight is 3600 Da, making it soluble in aqueous phase and fully digestible	Skin and joint health	[64]
NutripeptinTM	Copalis, France (Le Portel, Hauts, France)	Bioactive marine peptide	Reduces the glycaemic index of foods and thus helps to reduce fat storage in weight-control formulas	[65]
ProtizenTM	Copalis, France (Le Portel, Hauts, France)	Pollock and coalfish digest produced by enzymatic hydrolysis/anti-stress peptide that promotes well-being, found in Serenlider product—possess anxiolytic properties and is considered as beneficial for mental health/stress	Anti-stress, mood food, promotes restful sleep	[66]
Molval®	Dielen Laboratoire, France (Cherbourg-en-Cotentin, Normandy, France)	Extracted from cod and mackerel/Gabolysat PC60.	Beneficial effects on dyslipidaemia and cardiovascular risk, contains omega-3 fatty acids and Gabolysat PC60/anti-stress effects	[67]
Curcumega®	Dielen Laboratoire, France (Cherbourg-en-Cotentin, Normandy, France)	Fish oil rich in omega-3 fatty acids combined with turmeric	Nutritional impact and antioxidative effects	[67]
Seagest®	Trimedica, USA (Santa Monica, CA, USA)	Deep ocean within fish species		none found
PeptACE®	Natural factors, USA (14224 167TH Ave SE Monroe, WA, USA)	Bonito fish hydrolysate/nine small peptides derived from Bonito fish	Maintains normal blood pressure	[68]
Stabilium® 200	Nutricology, Canada (Salt Lake City, UT, USA)	Derived hydrolysate from Molva dypterygia	Improves resilience to stress, may reduce fatigue and supports normal psychological functions, such as memory, concentration, and cognitive abilities	[69]
Amizate®	Zymtech Production AS, Norway (Oppland, Lesja)	Enzymatic process extracts amino acids, short peptides, and micronutrients from Atlantic salmon (Salmo salar)	Excellent nutritive value; mood improving agent	[70]
WhiteCal®	BioMarine Ingredients Ireland (BII), Ltd. (Ballybay, Monaghan, Ireland)	Blue whiting fish/WhiteCal is a marine mineral complex, naturally rich in collagen peptides and high in calcium, phosphorus, and magnesium. It can be easily used in a wide range of human nutrition applications	Growth and repair of the body and maintenance of good health, bone, and joint health.	[71]
ProAtlantic®	BioMarine Ingredients Ireland (BII), Ltd. (Ballybay, Monaghan, Ireland)	Premium grade hydrolysed Fish Protein Isolates (FPI) containing 95% protein and 0.5% fat for human products	Glycaemic control, diabetes prevention, satiety	[72]

3. FPHs—As a Pet Health Food Ingredient

The use of FPHs in pet food exemplifies the intersection of advanced nutritional science and sustainable innovation. Valued at USD 1.4 billion in 2023, the market for fish-based pet health products is projected to surge to USD 16.7 billion by 2033, with an annual growth rate of 5% [73]. This growth is driven by rising pet ownership, the humanisation of pets, and a growing demand for premium, health-focused products [74]. Pet owners are increasingly willing to invest in diets offering superior taste, nutrition, and functional benefits [75]. FPH-based formulations are associated with enhanced digestibility, nutrient bioavailability, and multiple health advantages [76].

Age-related conditions in pets—such as inflammation, allergies, coat deterioration, and general health decline—also influence consumer preferences for fish-derived ingredients known to address these issues [77]. Moreover, sustainability concerns are shaping purchasing behaviour, with consumers seeking eco-friendlier alternatives to traditional meat-based pet foods [78]. FPH stand out for their hypoallergenic properties, high nutritional value, and alignment with sustainable resource utilisation [79]. FPHs are produced via enzymatic hydrolysis, a process that breaks down fish proteins into smaller peptides and amino acids, enhancing their digestibility and bioavailability—encompassing bioaccessibility, cellular uptake, and metabolic transformation [80,81]. This method also yields bioactive peptides that provide functional health benefits beyond basic nutrition [81]. They deliver a well-balanced amino acid profile, rich in essential amino acids such as lysine, methionine, and tryptophan—vital for muscle development, metabolism, and neurotransmitter synthesis in pets [82]. Their hypoallergenic nature makes them ideal for pets with food sensitivities, offering a superior alternative to conventional proteins like beef, chicken, or soy [83,84].

Moreover, FPH are highly palatable, enhancing food acceptance and consistent intake [85]. Certain peptides exhibit antimicrobial activity, promoting gut health by suppressing pathogenic bacteria [86,87,88,89,90], which is increasingly relevant due to the gut–brain axis’s influence on pet behaviour and neurological well-being [91]. Anti-inflammatory peptides present in FPH may also support the management of chronic conditions common in ageing pets [92,93,94,95,96]. Additionally, the collagen content in FPH supports joint health and mobility, with collagen peptides offering superior digestibility and bioavailability [97].

The production of FPHs exemplifies a sustainable approach rooted in circular bio economy principles, promoting the valorisation of fish processing by-products such as skins, bones, and viscera. This not only reduces the environmental impact but also enhances resource efficiency by converting waste into high-value ingredients for pet food [98,99].

FPH are produced through selective enzymatic hydrolysis and controlled fermentation, enabling precise modulation of peptide molecular weight and optimisation of bioactive properties [100]. In silico techniques further support this process by predicting the functional potential of peptides, particularly when integrated with in vitro hydrolysis methods [101]. These precision approaches enable the development of targeted pet food solutions for managing chronic conditions such as obesity, diabetes, and kidney disease. For example, low molecular weight peptides derived from fish have demonstrated antihypertensive effects, highlighting their role in preventing cardiovascular issues in pets [102,103].

With rising incidences of chronic ailments—such as cardiovascular disease, arthritis, digestive disorders, oxidative stress, renal dysfunction, and cognitive decline—often linked to ageing, poor diets, or genetic predisposition, FPH are gaining attention as a functional ingredient for health-oriented pet nutrition [8,104,105]. Rich in bioactive peptides and essential fatty acids like EPA and DHA, FPH exhibit anti-inflammatory, antioxidant, and immunomodulatory properties, offering a holistic strategy to enhance pet health, well-being, and longevity [106].

3.1. Cardiovascular and Hypertensive Health Issues

Cardiovascular disease (CVD) affects over 10% of dogs, with its incidence increasing by 1.5-fold annually [107]. Large, ageing dogs are particularly susceptible to dilated cardiomyopathy (DCM), while smaller breeds often develop degenerative mitral valve disease (DMVD), both of which contribute to significant veterinary costs and reduced quality of life [108]. Nutritional interventions—including coenzyme Q10, taurine, arginine, vitamin E, L-carnitine, and omega-3 fatty acids—have been shown to reduce inflammation, improve appetite, enhance cardiac function, and extend lifespan in affected dogs [109,110]. Fish-derived proteins and hydrolysates, rich in bioactive peptides and omega-3s, are increasingly recognised for their cardioprotective effects [111].

Pasławski et al. [112] reported that a fish-based diet enhanced cardiac and metabolic health in small-breed dogs with mitral valve disease. Similarly, Liu et al. [113] found that collagen hydrolysate from Atlantic salmon skin exhibited antioxidant, anti-inflammatory, endothelial-protective, and anti-platelet properties—comparable to aspirin—in atherosclerosis models. Key peptides, including FAGPPGGDGQPGAK and IAGPAGPRGPSGPA, reduced plaque buildup and arterial thickening in high-fat-fed mice. Maneesai et al. [114] further demonstrated that tuna protein hydrolysates (TPH) restored cardiovascular enzyme balance and reduced myocardial damage, oxidative stress, and inflammation in rats, yielding therapeutic effects comparable to metformin for managing obesity, hypertension, and hyperglycaemia.

Hypertension is another growing health concern in companion animals, particularly in ageing dogs and cats, often associated with chronic kidney disease, obesity, and diabetes [115]. Frequently asymptomatic in early stages, it can lead to severe complications such as heart failure, renal damage, and vision loss. The condition’s rising prevalence is closely tied to sedentary behaviour and poor diets, paralleling human trends [116]. Long-term treatment also imposes financial burdens on pet owners, prompting interest in natural, food-based interventions. Functional diets enriched with FPHs offer cardiovascular and antihypertensive benefits with minimal side effects [117].

Research supports the efficacy of FPHs in managing hypertension. In obesity-related renal insufficiency models, herring and salmon FPH significantly inhibited angiotensin-converting enzyme (ACE) activity, improved renal biomarkers, and demonstrated potent renoprotective effects. Herring and salmon hydrolysates yielded 81 and 49 ACE-inhibitory peptides, respectively. Obese Zucker rats on a 25% FPH diet exhibited decreased urinary protein, cystatin C, and glucose levels [118]. Aissaoui et al. [119] reported that red scorpionfish hydrolysates showed strong ACE-inhibitory and antioxidant activities. Likewise, Taheri and Bakhshizadeh [120] found that kawakawa FPH, especially peptides within the 1–3 kDa range rich in hydrophobic amino acids, possessed potent antioxidant and antihypertensive properties.

3.2. Arthritis

Arthritis is increasingly prevalent in ageing pets, impairing mobility, reducing quality of life, and leading to long-term veterinary costs [121]. In response, pet owners are turning to FPHs for their natural anti-inflammatory and joint-supporting properties, making them a promising dietary intervention for managing arthritis symptoms [122]. In a 16-week study on dogs with osteoarthritis (OA), deep sea fish oil significantly reduced malondialdehyde (MDA), a key marker of oxidative stress, and increased free carnitine levels—both indicators of improved metabolic health [122]. Compared to corn oil, fish oil also had more favourable effects on immune and metabolic markers, including reductions in specific white blood cells.

Manfredi et al. further demonstrated that a commercial fish-based diet enriched with fish oil fatty acids significantly reduced the incidence and severity of elbow dysplasia and OA in growing Labrador retrievers [123]. Similarly, studies on German shepherds with early-stage OA showed that collagen hydrolysates, sulphated glucosamine, and fatty acid-enriched diets (e.g., Hill’s JD) improved mobility and agility [124]. Researchers concluded that combining marine-derived nutraceuticals with vitamin- and lipid-rich diets offers the most effective joint health support in pets.

3.3. Hair and Coat Issues

Hair and coat disorders—such as shedding, dullness, and skin irritation—are common in pets and often stem from poor nutrition, allergies, or underlying conditions [125]. FPHs, rich in essential amino acids and omega-3 fatty acids, are increasingly used to promote skin and coat health. They help strengthen the skin barrier, reduce inflammation, and support hair growth, leading to shinier coats and healthier skin [126,127].

Fritsch et al. reported that Hill’s^® Prescription Diet^® Canine Skin Support, enriched with salmon protein and fish oil, significantly improved redness, skin thickness, and sores in 101 dogs with chronic pruritus, while owners noted reduced itching and better coat condition [128]. Noli et al. [84] reported that a hydrolysed fish and rice starch-based diet (Farmina Ultra Hypo—FUH) effectively alleviated skin allergy symptoms in dogs with pruritus while also modulating gut microbiota composition. The study highlighted that the FPHs reduced immune reactivity to dietary proteins, promoted beneficial gut microbes, and significantly eased allergic skin responses. Similarly, Szczepanik et al. demonstrated that a hypoallergenic diet with 18% hydrolysed salmon significantly reduced skin lesions and itching in dogs and cats with food-related allergic dermatitis, showing over 50% symptom reduction using clinical scoring systems [129]. These findings highlight the therapeutic role of FPH in managing dermatological issues in companion animals.

3.4. Digestive, Renal, and Metabolic Health Issues

Digestive disorders such as chronic enteropathy (CE) and inflammatory bowel disease (IBD) frequently affect pets, leading to symptoms like vomiting, diarrhoea, weight loss, and malnutrition. These conditions often result from abnormal immune responses to dietary or environmental triggers [130,131,132]. FPHs, composed of highly digestible and low-allergen peptides, have demonstrated efficacy in reducing gut inflammation and minimising immune activation [71,133,134]. CE, which includes food-responsive (FRE), antibiotic-responsive (ARE), and immunosuppressant-responsive (IRE) forms, is most commonly food-responsive. More severe forms, such as protein-losing enteropathy (PLE), pose greater risks due to protein loss and poor prognosis [134,135]. Diets based on hydrolysed or novel proteins have shown significant benefits in FRE and PLE cases [135,136].

Ontsouka et al. [137] found that a fish meal and potato protein diet enriched with omega-3 fatty acids reduced inflammation and improved fatty acid absorption in dogs with FRE and IBD. Simpson et al. [138] observed clinical recovery and sustained remission in PLE dogs fed hydrolysed fish-based diets, with notable gains in weight, serum albumin, and micronutrient levels. Zinn et al. [139] compared fish-based ingredients—including pink salmon hydrolysate, milt meal, and white fish meal—to poultry by-product diets in senior dogs, finding improved nutrient digestibility and reduced pro-inflammatory cytokines, underlining FPHs’ role in gut health and immune modulation.

Oxidative stress, resulting from an imbalance between reactive oxygen species (ROS) and antioxidant defences, contributes significantly to cellular damage, inflammation, and the progression of chronic kidney disease (CKD), particularly in ageing pets [140]. FPHs are rich in antioxidant peptides that combat oxidative stress, reduce inflammation, and support renal function, making them a natural dietary strategy for CKD management [141].

Nasri et al. [142] showed that goby FPH improved antioxidant status and metabolic markers in rats fed a high-fat, high-fructose diet, suggesting renal and glycaemic benefits. De Godoy et al. [143] reported that fish oil supplementation in lean Beagles increased ghrelin, stabilised body weight, and reduced oxidative stress, cholesterol, and glucose levels. Similarly, Riyadi et al. [144] demonstrated that tilapia viscera hydrolysate lowered oxidative markers and improved kidney structure in hypertensive rats. In working dogs, Ravić et al. [145] found that fish-based diets decreased blood glucose, LDL cholesterol, and oxidative stress while enhancing lipid profiles, supporting cellular health under physical strain. Additionally, Theysgeur et al. [146] used a canine gastrointestinal model to show that tilapia hydrolysates promoted secretion of appetite-regulating hormones (CCK and GLP-1) and inhibited DPP-IV activity, indicating potential for appetite control and obesity prevention in pets.

3.5. Cognitive and Emotional Health in Ageing Pets

Age-related memory decline and anxiety are increasingly recognised as significant concerns in ageing pets, particularly dogs and cats. Cognitive deterioration, often manifested through disorientation and behavioural changes, is linked to oxidative stress and neuro-inflammation—mechanisms similar to those seen in humans [147]. Functional diets enriched with FPHs, which are rich in neuroprotective and antioxidant bioactive peptides, are gaining attention for their potential to mitigate oxidative damage, support brain health, and slow cognitive decline.

Zicker et al. [148] demonstrated that beagle puppies fed DHA-rich fish oil from weaning to one year showed improved memory, learning, coordination, visual function, and immune response. Similarly, Pan et al. [149] found that fish oil supplementation in senior cats with cognitive dysfunction enhanced memory and reduced signs of brain ageing. Further research by Pan [150] showed that a Brain Protection Blend (BPB)—combining fish oil and L-arginine—improved task performance in older dogs, especially in spatial challenges. In ageing mice, Chataigner et al. [151] reported that a fish hydrolysate diet enriched with omega-3s enhanced memory, reduced anxiety, balanced stress hormones, and increased neurotrophic factors like NGF and BDNF.

Anxiety, often triggered by separation or loud noises, is another prevalent issue in dogs, presenting as excessive barking, destructive behaviour, and nervousness [152]. FPHs have demonstrated anxiolytic properties by modulating the hypothalamic–pituitary–adrenal (HPA) axis and enhancing GABA activity, mirroring pharmaceutical interventions [153]. Bernet et al. [153] showed that Gabolysat^® PC60 significantly reduced stress hormone release in rats, with Freret et al. [154] noting anxiolytic effects comparable to diazepam. Landsberg et al. [152] found that sustainable white fish-derived hydrolysates reduced anxiety and cortisol in dogs during simulated thunderstorms. Titeux et al. [155] observed improved stress resilience and sociability in fearful dogs following GABOLYSAT^® PTP 55 supplementation.

In cats, Jeusette et al. [156] reported that a diet containing sardine peptides, lemon balm, oligo fructose, and L-tryptophan reduced urinary cortisol more effectively than L-tryptophan alone. Porcheron et al. [157] demonstrated that Zylkene Plus, a white fish hydrolysate, significantly decreased separation-related anxiety in dogs, with 49% showing behavioural improvement. Ephraim et al. [158] linked fish oil to reduced anxiety-related metabolites and increased beneficial gut bacteria in senior dogs. Dinel et al. [159] showed that Peptidyss^®, a sardine-derived hydrolysate, lowered corticosterone and regulated stress-related gene expression in mice. Collectively, these studies highlight the dual role of FPHs in supporting cognitive function and emotional well-being in pets, making them a promising natural strategy for improving the quality of life in ageing companion animals. Commercialised products marketed as functional ingredients/products for pet health are shown in

Table 2. Bioactive ingredients/hydrolysates marketed for pets available commercially.

Product	Manufacturers	Ingredients/Raw Material	Product Description	Specific Features
Salmigo® Protect L60	Biomega (Skogvåg, Vestland, Norway) [160]	Fresh, high-quality Atlantic salmon leftovers	– Liquid salmon peptide – Produced using patented non-GMO enzymatic process – Food-grade, preservative-free formulation – Clean-label, natural protein source	– 90% protein content – Rapidly absorbable bioactive peptides and amino acids – Enhances nutrient delivery to body tissues – Supports feline-specific nutritional needs
Salmigo® Active		Fresh, high-quality Atlantic salmon leftovers	– Salmon peptide powder – Made via patented non-GMO enzymatic hydrolysis – Food-grade, preservative-free and naturally processed	– Promotes skin, coat, joint, and overall pet well-being – Highly digestible, absorbable protein source (>70% peptides and free amino acids) – Delivers high biological value nutrition
Dog Adult Dermal Hydrolysed Fish	Trovet + Plus (De Vergert 4, 6681 Le Bemmel, Netherlands) [126]	White FPHs, rice, potato, apple, fish oil, linseed, minerals, borage oil	– Low molecular weight hydrolysed protein (<10,000 Da) – Nutritional profile: protein 8%, fat 7%, fibre 0.75%, ash 2.5%	– Supports skin health in pets with dermatosis and hair loss – Reduces inflammation and allergic reactions – Promotes skin barrier strength, fur vitality, and overall dermal function
Cat Intestinal Fresh Hydrolysed White Fish		Extruded rice, rice protein, hydrolysed white fish, fish oil, sunflower oil, hydrolysed fish, krill Antarctic, apple fibre, vegetable fibres, psyllium, hydrolysed yeast cell wall, and inulin	– Single animal protein source – Nutrient profile: 32% protein, 20% fat, 2.75% fibre, 6.50% ash	– Minimises ingredient and nutrient intolerances – Supports compromised digestion – Promotes skin health and reduces excessive hair loss – Enriched with prebiotics
Multi-Purpose Treat for cats (Hydrolysed Protein)		Rice, salmon protein (hydrolysate), sodium chloride, sugar, collagen (hydrolysate), cellulose, poultry fat	– Hypoallergenic treat with a single hydrolysed protein (fish) source – Nutrient profile: 30% protein, 8% fat, 5.5% ash, 2.5% fibre	– Prevents both food allergies and intolerances that cause skin issues – Reduces risk of digestive problems like diarrhoea and vomiting – Supports prevention of chronic kidney (renal) insufficiencies
Sensitive Soft Chews Salmon	Optima Nova (ARGANDA DEL REY, Madrid, Spain)	Salmon and salmon by-products, tapioca and potato, and fats	– Grain free functional snacks for dogs – Nutrient profile: protein 35%, fat 5%, fibres 2%, ash 10.5%	– Easily digestible functional snacks with hypoallergenic ingredients – Ideal for dogs with sensitive skin or digestive issues
Adult Sensitive Salmon and Potato		Fresh, ground, hydrolysed salmon, dehydrated potato, potato protein, oil, sugar beet meal, yeast, FOS, MOS	– Balanced and complete nutrition for dogs – Hypoallergenic – Gluten free formulation – Nutrient profile: protein 27%, fats 16%, fibre 2.75%, ash 7%	– Supports dogs with food intolerances and allergies, improving skin and digestion – Provides healthy skin, shiny coat, and enhanced heart, immune, and nervous system function – Potential anti-cancer benefits
Medica Hypoallergenic PLUS Salmon for dogs	Select Gold (Germany)	Potato flakes, salmon protein, hydrolysates, hydrolysed poultry liver fish oil, potato protein, sunflower oil, poultry fat	– Single, partially hydrolysed, animal protein source – Nutritional profile: protein 23.5%, fat 16.5%, ash 6.8%, fibre 2.6%	– Assists dogs with food sensitivities and allergies – Alleviates initial symptoms of intolerance – Provides balanced and complete nutrition
Medica Hypoallergenic PLUS Fish and rice for cats		Rice, potato protein, hydrolysed fish protein, poultry fat, potato starch, dried beet pulp, beef fat, cellulose, sardine oil, hydrolysed poultry liver, salmon oil, and linseed oil	– Single, partially hydrolysed, animal protein source – Nutritional profile: protein 33%, fat 18%, ash 6%, fibre 3.3%	– Minimises nutrient intolerances and food allergies in cats – Supports skin function in dermatosis – Reduce inflammation in sensitive cats
Functional treats—sensitive protein	Boxby (Berltsum, Friesland, Netherlands)	Hydrolysed salmon, potato flakes, rice meal, omega-3 fatty acids, propylene glycol, omega-6 fatty acids	– Hydrolysed salmon proteins – Free from wheat and soya – Nutritional Profile: protein 23%, fat 5%, fibre 1%, ash 2%	– Reduces unwanted dietary allergies and intolerances in dogs – Supports skin and coat health
SEACURE®—Daily protein supplement for dogs	Proper Nutrition (West Chester, PA, USA).	Made from Pacific whiting caught in the Pacific Northwest	– Enzymatically hydrolysed proteins – Rich in amino acids and peptides – Protein supplement for overall health – Nutritional Profile: protein 60%, fibre 5%, fat 2%	– Enhances overall health for puppies, adults, and sick or elderly dogs – Boosts immune function – Promotes healthy skin and coat – Alleviates food intolerance symptoms
HY Food Allergen Management	Specific Cat FDD (Dechra, Northwich, UK)	Rice, rice protein, hydrolysed salmon protein, pork fat, cellulose, protein hydrolysate, fish oil, psyllium husks, rosemary extract	– Specially formulated for sensitive cats with ingredient intolerances – Nutritional profile: protein 27.5%, fat 12.5%, fibre 3.3%, ash 7.2%	– Supports a healthy immune system – Helps maintain normal urinary tract function – Relieves acute intestinal malabsorption – Aids digestion and supports pancreatic function
Veterinary HPM® Hypoallergic dog foodwith hydrolysed fish protein	Virbac UK (Woolpit, Bury, Suffolk, UK)	Potato starch, hydrolysed fish protein, animal fats, lignocellulose, minerals, hydrolysed pork and poultry proteins, beet pulp, FOS, mono di and triglycerides of fatty acids, Lactobacillus acidophilus	– Elimination diet for adult and senior dogs – Contains 97% peptides <10 kDa (mean molecular weight: 1.82 kDa) for optimal digestibility – Nutritional profile: protein 24%, fat 18%, fibre 4.5%, ash 7%	– Provides natural dermal defences – Reduces the risk of other allergies – Maintains a healthy coat – Helps with gastrointestinal functions
Vet Life Cat Ultra hypo	Farmina Pet Foods (Essex, UK) [84]	Rice starch, hydrolysed fish protein, fish oil, potassium chloride, calcium carbonate, mono-di-calcium phosphate	– Developed without vegetable proteins for food allergies or intolerances – Nutritional profile: protein 18%, fat 15%, fibre 1.2%, ash 5.3%	– Hypoallergenic and highly digestible formula – Supports a healthy immune system and natural skin barrier
Feline c/d stress urinary care—ocean fish	Hill’s® Prescription Diet® [124,128]	Brewer’s rice, ocean FPHs, chicken- and turkey meal, maize gluten meal, animal fats, tuna fish meal, soya bean oil, minerals, fish oil, linseeds	– Nutritional Profile: protein 33.3%, fat 15.2%, fibre 0.6%, ash 5.2%	– Reduces risk of urinary tract issues and urinary stone formation – Contains protein hydrolysates and L-tryptophan to support emotional balance
Canine skin support potato salmon formula		Salmon proteins, potato protein, potato starch, pork fat, soybean oil, pork flavour, fish oil, fish meal.	– Nutritional Profile: protein 18.4%, fat 15.5%, fibre 1.86%, total omega-3 FA 1.41%	– Supports healthy skin, coat, digestion, and immune system
Natural veterinary diet hf hydrolysed intolerance, salmon, dry cat food	Blue Buffalo (Wilton, CT, USA)	Salmon hydrolysate, peas, potatoes, pea starch, canola oil, pea protein, flaxseed, pea fibre, fish oil, pumpkin, dried kelp, oil of rosemary.	– Formula for cats with sensitive stomachs – Nutritional Profile: protein >30%, fat >14%, fibre <4%	– Minimises adverse food reactions in cats with food intolerances – Supports healthy skin, coat, digestion, and immune system
Pure mackerel hydrolysate	iQi—Trusted pet food ingredients (MG Amersfoort, The Netherlands) Fiordo Austral (Calbuco, Chile) & ORIVO (Molde, Norway)	Mackerel processing side streams	– Spray-dried hydrolysate with over 71% protein and less than 10% ash – Rich in EPA and DHA for added health benefits	– Highly digestible with high protein and low ash content – Supports joint health, mobility, and promotes healthy skin and coat in cats and dogs
Pure salmon hydrolysate		Salmon processing side streams	– Rich in protein (minimum 72%) and essential nutrients. – Can be directly applied to pet food for enhanced nutrition	– 99% protein digestibility and low ash content – Meets hypoallergenic food standards with broad health benefits for cats and dogs
Pure sardine hydrolysate		Sardine processing side streams	– Spray—dried powder – Hydrolysate that contains over 71% protein	– Superior digestibility – High protein and lower ash – Contributes to healthy joints and overall mobility
Pure tuna hydrolysate		Tuna processing side streams	– Fine spray-dried tuna hydrolysate powder offers superior quality compared to rendered meal – Ideal for low-temperature processing applications	– Hypoallergenic with highly digestible protein – Rich in omega fatty acids – Supports brain development, ideal for young animals
Veterinary diet—hypoallergenic	[129]	Dehydrated salmon, yellow peas, hydrolysed salmon protein, buckwheat, salmon oil, hydrolysed salmon gravy, minerals, dried Ascophyllum nodosum, MOS, FOS	– Hypoallergenic grain-free food – Nutritional profile: protein 27%, fat 14%, fibre 2%, ash 7.2%	– Ideal for dogs with chronic diarrhoea, IBD, or skin issues – Reduces allergic reactions and supports gut health

.

4. FPHs as Pet Palatants

In 2023, the worldwide pet food industry was valued at USD 120.87 billion. Forecasts indicate an expansion from USD 126.66 billion in 2024 to USD 193.65 billion by 2032, reflecting an annual growth rate of 5.45%. North America led the market in 2023, accounting for 42.55% of the market share (https://www.fortunebusinessinsights.com/industry-reports/pet-food-market-100554 (accessed on 23 September 2024)) [161]. Palatants also substantiate a crucial vertical of the pet food industry as this class of products play a vital role in influencing pets’ acceptance and preference for their food. These additives are incorporated into pet foods to enhance their taste and aroma, making them more appealing to animals [162]. The effectiveness of palatants is crucial in ensuring consistent consumption, especially among precise eaters or pets with specific dietary needs. In today’s competitive market, where pet owners increasingly prioritise high-quality, nutritious, and appealing food options for their pets, the inclusion of palatants can determine a product’s success [163]. The science behind palatants involves understanding animals’ sensory preferences and developing formulations that improve the overall palatability of pet food. This approach supports better nutrition and health outcomes for pets by encouraging them to consume food enriched with essential nutrients [163,164]. Overall, palatants play a pivotal role in the pet food industry, enhancing the quality and attractiveness of pet food products while promoting better dietary habits and overall well-being for pets. The market for pet food palatants was valued at $1981.2 million in 2023 and is expected to grow at a compound annual growth rate of 6.5% from 2024 to 2030 [165]. The appeal of pet food is influenced by numerous elements, such as the freshness of its components, the texture, size, and shape of the kibble, and particularly the use of palatants. Palatability is not only a critical component of pet nutrition, but also a key driver of brand loyalty. Palatants often consist of volatile and soluble compounds, including amino acids, peptides, and lipids [163]. These substances are typically obtained from animal by-products and fish through processes like acid hydrolysis, enzymatic treatment, or thermal liquefaction. Animal digests or hydrolysates that are partially hydrolysed animal parts in both dry and liquid forms are used as palatability enhancers or palatants in pet feeds. They are defined by the Association of American Feed Control Officials (AAFCO) (AAFCO) as “a material which results from chemical and/or enzymatic hydrolysis of clean and undecomposed animal tissue. The animal tissues shall be exclusive of hair, horns, teeth, hooves, and feathers, except in such trace amounts as might occur unavoidably in good factory practice and shall be suitable for animal feed. If it bears a name descriptive of its kind or flavour(s), it must correspond thereto” (Animal Proteins Prohibited in Ruminant Feed and Cattle Materials Prohibited in All Animal Feed, WSDA). Indeed, salmon protein hydrolysate is a well-known palatant product with documented evidence suggesting that it improves food consumption by dogs and cats [166].

Palatability is the physical and/or chemical attribute(s) of the diet of an animal, involving the promotion or suppression of feeding behaviour during the pre-absorptive period. It relates to pleasure perception or liking during consumption. Palatable foods/feeds are ones that acceptable to the companion animal. Palatants incorporate many different macro- and micro-molecules including proteins, amino acids, carbohydrates, fatty acids, peptides, vitamins, and minerals. The aim of these ingredients is to enhance the sensory experience of the animal, and this relates to the umami T1R1 and T1R3 taste receptors [167].

Cats have affinity for umami compounds. In the pet food industry, animal protein hydrolysates can create palatability enhancers via the Maillard reaction. Digests or palatants are proteins that are enzymatically broken down and applied to dry feeds to provide a sensory impact (usually meat flavoured). The Maillard reaction is the chemical reaction between amino acids and reducing sugars to create melanoidins (high molecular weight polymers or sugars). Melanoidins give food and feeds their distinctive flavour [168]. Additionally animal proteins, as well as specific amino acids, animal fats, and emulsified meats, are important flavours that are highly palatable to cats. Hydrolysis releases compounds directly from raw materials like proteins, which are not volatile and/or sapid. These compounds (like peptides derived from proteins) can react with sugars and other peptides if a thermal treatment is applied. The Maillard reaction requires temperatures > 80 °C. This reaction generates flavour compounds. Their nature, origin and chemical formulas determine the specific aroma of the product. Modification of the process and the raw material used to produce the palatability enhancers directly affects the generation of tastes and flavours. Palatants are delivered to the consumer (pet food manufacturers or directly to pet owners) in liquid or powder form.

4.1. Palatant Form

Palatants exist in both dry and liquid forms and their addition to kibbles following extrusion can enhance the flavour of pet feeds. They are used widely, and large markets exist in the USA, Australia, France, Japan, and Chile. Wet pet foods have higher palatability than dry foods due to their higher moisture content and processing techniques. The inclusion level of palatants in wet pet feed are generally lower than those in dry pet feed [169]. They can be poured or dusted on the surface of cat or dog kibbles [164]. The palatability of the final product is evaluated directly by the animal. Pet preferences for one or another product is determined by a trained panel of pets, i.e., cats or dogs, using different methodologies of food presentation, as could be done with humans [163,164]. Adopting palatants in emerging pet food markets are beneficial to pet feed manufacturers and their brands (as well as pets). As consumption of pre-packaged pet food grows, flavour requirements for the food become more important.

4.2. The Difference Between Cats and Dogs

An animal’s sense of taste can help them assess the nutrient content of feed and helps protect them against eating things that might harm them. Moisture or water content of a food plays a key role in palatability for both dogs and cats, both of which generally prefer moist foods (i.e., wet, fresh) rather than dry foods (kibble) as the moisture content of wet foods is more like fresh meat [170]. Cats are obligate carnivores and require protein in their diet to thrive and survive. They prefer foods with high protein, especially animal proteins, which ensures that they are meeting their dietary requirements. Cats have less preference for carbohydrates and fat and usually prefer higher protein containing foods/low carbohydrate diets when given the option. Most commercial dry pet feeds contain prominent levels of carbohydrates since they are critical for successful extrusion processing, whereas wet feeds and emerging fresh-cooked formats typically contain higher amounts of meat, making them naturally more palatable compared to kibble. Dogs are omnivores and are more opportunistic with their feed selection. Importantly, like humans, dogs require amino acids from protein to survive. Dogs (like humans) often show preference for foods with simple sugars and higher fat content for energy. Where there is a crude fibre increase in the diet there is a decrease in palatability of pet feeds for dogs [170].

Cats have a preference for umami flavours and respond to nucleotides and L-amino acids. L-histidine when metabolised leads to the production of glutamate and it is known that in combination with nucleotides acts as a palatant enhancer. Other L-amino acids are thought to decrease palatability while L-phenylalanine, L-tyrosine, L-tryptophan, L-methionine, L-arginine, L-isoleucine, L-leucine, L-serine, and any combination of these in an effective amount of between 0.001 and 0.8 wt. percent on dry matter enhance palatability of dog food for dogs.

4.3. Marine Hydrolysates as Pet Palatants

Recently, Guilherme-Fernandez and colleagues explored the use of squid meal and shrimp hydrolysate as a protein source for dogs [171]. Chemical composition, antioxidant activity, and palatability was evaluated by comparing a commercial diet with the inclusion of 150 g kg−1 of squid meal or shrimp hydrolysate in diets fed to Beagle dogs (2.2 ± 0.03 years). The Shrimp hydrolysate displayed a greater antioxidant activity than squid meal and the preference in terms of the First approach and taste were not affected by the inclusion of these hydrolysates, but dogs showed a preference for the basal diet. Kemin produce a pet palatant from salmon and the French company Copalis^® produce CPSP^® soluble fish protein concentrates that claim to provide optimum palatability and contribute to animal well-being. Other palatant products, some derived from fish, are listed in

Table 3. Palatant product produced from fish and other animal and plant sources.

Product	Manufacturers	Market Presence	Ingredients/Raw Material	Product Description	Specific Features	Average Price Point (per 200 kg)
PalasuranceTM	Kemin (palatants produced in (De Moines, IA, USA, (Cavriago RE), Italy, and Macuco, Valinhos, Brazil)	Europe, USA, Australia	Salmon, lamb, beef	Available in both dry and liquid forms	– Support the unique protein trend/claim in pet food – Deliver desired level of palatability on the surface of kibble	USD 6.29 (per kg)
PalivateTM		Europe, USA, Australia	Duck, chicken, salmon, soy, lamb	Palatant for wet pet foods meeting flavour, pH, and texture expectations	– Withstand retort process for wet pet food applications – Low inclusion rate in multiple food formats (loaf/chunk/gravy) – Minimise effects to product integrity	>USD 6.29 (per kg)
PaltevaTM & Palteva PTM		Europe, USA, Australia	Duck, chicken, salmon, turkey, lamb, plant proteins	Natural flavour addition to pet diets	– Naturally, sourced flavour. – Naturally stabilised and preserved – Animal or plant-based products. – Super premium palatant in canines	>USD 6.29 (per kg)
Fish cream (cat food palatant)	Matchwell Nanjing Pet Products Supply Co., Ltd. (Nanjing, Jiangsu, China)	Available globally—online network	Ocean fish	Brown liquid, Crude protein (>15%), ash (<10%), moisture (<70%)	– Made from natural materials – Contains compound amino acid that boost immune system – Helps increase cats’ appetite – Enhance cat food palatability	USD 2.00/barrel
Seafood liquid palatant		Available globally—online network	Seafood		– Liquid form, brown in colour – Appeal booster innovation flavouring agent	USD 38.00 per barrel
CPSP® 90 and CPSP® G	Copalis Sea Solutions ® (Hauts, France, Symrise®, Teterboro, NJ, USA)	Europe and Asia	All fish—salmon and whitefish	Fine powder and liquid, soluble fish protein concentrates and hydrolysates, high value ingredient	– Strengthen the immune system – Consistent supply of bioavailable proteins – Improves the growth and development of young animals, pets and farmed fish	Unknown
Range of palatants from fish, animal proteins	AFB International ® (St. Louis, MO, USA).	Global—US based company	Fish, chicken, pork, turkey, duck, lamb, and non-meat protein	Liquid and dry no-GMO, grain free, non-soy, non-wheat, gluten free and clean label palatant products	– Helps customers develop new pet food products and improve existing ones – No artificial flavours, colours, or preservatives – Responsibly sourced fish based palatant products	Depends on the form of the product
ProShore—Fish protein Concentrates (FPC) and Fish Protein Isolate (FPI)	BioMarine Ingredients Ireland (BII) (Ballybay, Monaghan, Ireland).	Western Europe; Eastern Europe; Middle East; Asia; Australia; North America; Africa; Central/South America	Unknown	High quality liquid and powdered ingredients for premium pet food formulations	– High-grade FPI and FPC containing 55%–90% protein – Proteins enables repair and building of muscle – Has excellent molecular weight profiles	Unknown
ProAtlantic—FPH			Unknown	Spray dried, free flowing with a neutral odour, and superior solubility	– Contains 95% protein and 0.5% fat – Excellent amino acid profile – Improves growth and repair of the body and maintenance of good health – Consists of low molecular weight peptides	Unknown
PetSavio™ PPP 400	Essentia Protein Solutions (Oak Tree Court Ankeny, IA 50021 USA)	Global—US based company	Plaice	Paste form with protein (39%), fat (0.6%), ash (<10%)	– Enhances flavour – Brings specific flavour directions – Boosts the pet food formulation’s taste – Reduced fat content	Unknown
PetSavio™ PCP 400		Global—US-based company	Cod	Paste form with protein (40%), fat (1%), ash (9.5%)		Unknown
Seasoning Creame for cats (YCG-MT-915)	Jiangsu Yichong Biotechnology Company Limited (Suqian, Jiangsu, China)	Global—China-based company	Ocean fish, chicken liver, compound amino acids	Crude protein (>10%), ash (<10%)	– Ocean fish significantly trigger a cat’s taste – Helps in increasing appetite – Enhances the palatability – Compound amino acids to boost immune system	Unknown
Seasoning powder for cats (YCF-MT-02)		Global—China-based company	Ocean fish, chicken liver, Brewer’s Yeast, acidity regulator	Crude protein (>30%), crude fat (<20%), Ash (<45%)	– Ocean fish triggers cat’s taste – Cat food flavour enhancer – A tawny powder with good fluidity – Helps in increasing appetite and palatability	Unknown
Fish cream for cats		Global—China-based company	Ocean fish, compound amino acids, Brewer’s Yeast, Protease	Deep brown colour product, crude protein (>10%), ash (<10%)	– Compound amino acids are added to boost immune system – Helps increase appetite and enhance the palatability	Unknown

.

5. FPHs—Based Aquaculture Feeds

Aquaculture feeds are specifically designed to address the nutritional needs of aquatic species, combining various ingredients such as marine by-products, fish oils, plant-based components, live feeds, and vegetable proteins [172]. These feeds offer a balanced diet, supplying essential nutrients like proteins, vitamins, minerals, carbohydrates, and lipids that are vital for the growth, development, and reproductive health of fish and other aquatic organisms, ensuring their overall well-being [173]. The global aquaculture feed market has experienced remarkable growth, driven by the rising demand for seafood and the need for sustainable, high-quality feed solutions across a broad spectrum of species, from finfish to crustaceans [174]. In 2023, the global aquaculture feed market reached 49.70 million tonnes and is expected to rise to 78.93 million tonnes by 2032, with a steady CAGR of 5.3% from 2024 to 2032 [175]. The expanding aquaculture industry, heightened health awareness, increased seafood consumption, and a growing focus on sustainable fish production drive this market growth. As people recognise the health benefits of fish, including its rich protein content, omega-3 fatty acids, vitamins, and minerals, the demand for aquaculture feed has risen sharply [175,176]. Additionally, fish’s reputation as a healthier option compared to red meat due to its lower saturated fat levels has further fuelled the market’s expansion [177].

Manufacturers are increasingly turning to FPHs as a key ingredient due to their exceptional palatability, digestibility, and bioavailability, and ability to enhance growth, immune function, and nutrient absorption in aquatic species especially during early developmental stages or under stress conditions [178]. The primary mechanisms underlying FPH efficacy relate to their rapid absorption and multifaceted biological activity. Due to their short peptide length, FPHs bypass the need for extensive enzymatic digestion, allowing for faster uptake through peptide transporters (e.g., PepT1) in the intestinal epithelium [179,180]. This rapid nutrient assimilation contributes to improved feed efficiency, weight gain, and muscle accretion. Moreover, bioactive peptides in FPHs exert antimicrobial, antioxidant, immunomodulatory, and anti-inflammatory effects [180].

In terms of product development, the quality and functionality of FPHs depend on the choice of raw materials (e.g., fish offal, heads, viscera), hydrolysis conditions (enzyme type, temperature, pH, duration), and downstream processing techniques such as ultrafiltration and spray drying [181]. Commercial products such as Symrise Aqua Feed’s hydrolysates (derived from tuna, krill, and shrimp) and CPSP (Copalis Sea Solutions^®) have shown consistent efficacy in improving gut histomorphology, nutrient digestibility, and pathogen resistance [182,183,184,185]. Furthermore, FPHs have enabled partial replacement of traditional protein sources like fish meal or soy protein concentrate by up to 50–60% without compromising performance, contributing to circular bio economy models in the aquafeed industry [186]. As a result, FPHs are emerging as a preferred choice for both economic and environmental reasons in the aquaculture industry.

Early evidence by Refstie et al. [187] showed that replacing part of the fish meal with FPHs made from fresh Pollock body parts (Denofa Fish Peptides, Denofa, Fredrikstad, Norway) in Atlantic salmon diets improved feed intake, growth, nutrient retention, and digestibility in a dose-dependent manner—likely due to increased palatability and peptide-driven nutrient assimilation. This pattern was echoed in subsequent studies, where the molecular weight and peptide composition of hydrolysates played a critical role in physiological outcomes. For instance, Kotzamanis et al. [185] found that a commercial hydrolysate (CPSP, Copalis Sea Solutions^®) with peptides ranging from 500 to 2500 Da significantly enhanced growth and intestinal development in sea bass larvae, likely through stimulation of digestive enzyme activity and improved gut maturation.

Tang et al. [188] and Zheng et al. [189] further linked FPH inclusion to enhanced growth and immunity in large yellow croaker and Japanese flounder, respectively. Improved weight gain and immune parameters (e.g., lysozyme, immunoglobulin M) were associated with increased bioavailability of peptides and their immunomodulatory effects. Notably, ultra-filtered fractions rich in low molecular weight peptides were most effective, suggesting that smaller peptides more readily activate endocrine and metabolic pathways such as IGF-I, crucial for growth regulation.

This metabolic efficiency is evident in species like barramundi. Chaklader et al. [180] tested FPHs derived from yellowtail kingfish, carp, and tuna (Specialty Feeds, Glen Forrest, Australia), while Siddik et al. [190] evaluated tuna-based FPHs (SPF Diana Co. Ltd.), both reporting significant improvements in growth, fillet quality, and immune function. These benefits were linked to elevated polyunsaturated fatty acid levels, enhanced gut barrier integrity, and robust systemic immune responses, including greater resistance to Vibrio harveyi infection. Additionally, reduced hepatic and renal stress markers highlighted the hepatoprotective and anti-inflammatory potential of FPH supplementation. Similar benefits were recorded in shrimp, where Gunathilaka et al. [182] demonstrated that FPHs (Symrise Aqua Feed, Specialities Pet Food, France) improved feed efficiency, digestibility, carcass lipid content, and antioxidant status. The bioactive peptides likely improved intestinal absorptive capacity and cellular oxidative defence, supporting tissue repair and energy metabolism.

In Channa striata, Siddaiah et al. [191] and Suratip et al. [192] reported enhanced weight gain, blood profiles, and immune activity, including increased lysozyme and myeloperoxidase levels. These improvements were linked to elevated haemoglobin and serum proteins, reflecting systemic immune stimulation and better nutrient transport—key for robust disease resistance and survival. Tuna hydrolysate supplementation in Asian sea bass diets showed improved growth, feed efficiency, and protein utilisation (Tola et al. [193]). The observed enhancement in diet palatability and nutrient digestibility enabled a substantial replacement (up to 55%) of fish meal with plant protein sources without compromising performance. This underscores FPH’s role as a functional dietary enhancer that mitigates the antinutritional effects of plant ingredients.

Suma et al. [194] demonstrated similar outcomes in Ompok pabda, where a 2% inclusion of FPH yielded optimal growth, survival, liver function, and immune responses. Improved hepatosomatic index and condition factor were attributed to enhanced feed intake and efficient metabolic conversion. In salmonids, Sandbakken et al. [195] confirmed that enzymatically produced salmon hydrolysates improved protein and amino acid digestibility, mineral absorption, and overall growth. These outcomes reflect the hydrolysate’s ability to bypass typical digestive constraints and supply essential nutrients in highly available forms.

Recent studies in 2024 reinforced these trends. Sezu et al. [183] reported that a 7% inclusion of FPH (Symrise Aqua-Feed, Specialities Pet Food, France) in Ompok pabda broodstock diets not only improved growth and feed conversion but also significantly enhanced reproductive performance—including fecundity, spawning response, and egg fertilisation—likely due to improved energy partitioning and endocrine support. Kabir et al. [184] showed that Nile tilapia fed hydrolysate-enriched (Symrise Aqua Feed, Specialities Pet Food, France) diets displayed superior liver and gut morphology, stronger immune cell populations, lower excretory waste, and enhanced resistance to Streptococcus iniae, translating into improved farm economics.

Despite promising outcomes, several research gaps remain. The specific peptide sequences responsible for the observed biological effects are often poorly characterised, limiting the precision of functional feed design. Furthermore, the interaction between FPHs and host microbiota is not fully understood—though evidence suggests FPHs can shape microbial communities in ways that enhance disease resistance and nutrient metabolism [180].

Another area requiring attention is species-specific response variability; for instance, FPHs that work well in carnivorous marine fish may not yield similar benefits in omnivorous freshwater species. Additionally, while short-term trials demonstrate clear advantages, long-term effects on fish health, reproductive performance, and fillet quality need further elucidation. There is also a need to develop standardised testing protocols and molecular biomarkers to assess the functional efficacy of FPHs in vivo. Finally, cost-effectiveness and scalability remain critical concerns for commercial uptake [178]. Advanced bioprocessing technologies, such as membrane separation and fermentation-aided hydrolysis, may help address these challenges by increasing peptide yield and functional consistency [179]. Overall, FPH-based feeds hold immense potential, but fully leveraging their benefits requires deeper mechanistic understanding, product optimisation, and integrative research approaches.

Table 4. Manufactures of FPHs used in the manufacturer of aquaculture feeds.

Product	Manufacturers	Ingredients/Raw Material	Product Description	Specific Features	References
Actipal™ (Fish hydrolysate for fish and shrimp)	Diana Group S.r.L (Treviso, Italy)	Locally sourced, 100% fish side-stream	– Made in Costa Rica – Enzymatically hydrolysed – Contains free amino acids and bioactive peptides	– Bioactive peptides enhance resistance to stress and pathogens – Boosts immunity and growth hormones – Supports steady feed intake during stress, diet shifts, and growth stages – Maintains optimal health and performance	Gunathilaka et al. [182] Suma et al. [194]
Nutri™ Tuna (Tuna hydrolysates)		Locally sourced, 100% side-stream tuna	– Made in Indonesia – Contains highly soluble free amino acids and highly bioavailable short peptides	– Maintains a high level of feed intake throughout the rearing cycle – Helps in stressful events or changes in feed formula – Improves feed palatability, digestibility, efficiency and growth	Tola et al., [193]
Nutri™ Tuna Soluble extract (TSE)		Locally sourced, 100% side-stream tuna	– Made in Thailand – Highly digestible proteins – Attractive palatable product for fish and shrimp feeds	– Produced using resources from certified fisheries through a standardised process to guarantee optimal freshness and product consistency – Soluble and highly digestible protein source for fish and shrimp feed – Contains a high level of palatable amino acids that increase attractant properties	Suratip et al. [192]
Nutri™ Tuna Liver powder (TLP)		Locally sourced, 100% side-stream tuna	– Made in Thailand – Offers digestible proteins and high-quality fats	– Provides a full range of amino acids and high-quality fats – Naturally palatable and attractive to aquatic species. – Boost palatability and performance in the early growth stages of fish and shrimp
ProShore	Bio Marine Ingredients (Ballybay, Monaghan, Ireland)	Premium FPHs	– Optimal for hatchery and fish farming – It has impressive protein peptide and mineral profiles with superior solubility	– Boosts the growth and development rate of cultivated freshwater and saltwater populations – Contains high protein content – Enables growth enhancement and immunity enrichment
Fish Protein Hydrolysate Liquid	Janatha Fish Meal & Oil Products (Kota, India)		Liquid FPH with ≥40% hydrolysed protein	– Enhances growth, survival, and larval development – Reduces the incidence of skeletal deformities – Improves larval quality in both freshwater and marine fish species – Act as feed attractant, thus enhancing the palatability and acceptance of the feed	Siddaiah et al. [191]
Fish Protein Hydrolysate Powder			Powder FPH with ≥80% hydrolysed protein	– Protein fractions with weight between 1 and 10 kDa enhance feeding activity in fish larvae – Peptides with lower molecular weight (0.2 to 2.5 kDa) beneficially affect larval growth and survival – Enhances the activity of digestive enzymes in the intestine
Fish Soluble Paste (Super attractant)			Liquid FPH with ≥60% hydrolysed protein	– Helps in growth simulation – Hydrolysed proteins have better palatability, nutrition and bioactivity – Works as a feed attractant and organic fertiliser
ScanPro™	Scanbio Marine Group AS (Brattørkaia, Trondheim, Norway)	Norwegian salmon, pelagic and white fish	Enzymatically hydrolysed and concentrated fish protein is an excellent economical ingredient for feeds	– Highly digestible and hypoallergenic – Assimilation of peptides offers maximum nutritional value – Helps in growth simulation of fish larvae
Natural Nautic®	Omega Protein Corporation (Reedville, VA, USA)	Menhaden	Fish meal is a high-quality protein made from menhaden and is naturally stabilised with mixed tocopherols	– Complete source of highly digestible, low-allergenic protein – Has a superior amino acid profile – An excellent source of omega-3 fatty acids and natural protein for fish
Special Select®		Menhaden	Premium fish meal is a high-quality protein made from menhaden
SeaLac®		Menhaden
Hydrolysed Salmon Protein	Sociedad Pesquera Landes Sa (Talcahuano, Chile)	By-products of the Chilean salmon industry	A perfect ingredient for fish nutrition with 71% protein, 20% lipids, and > 98% digestible	– Ideal for improving palatability – Easy to digest – Excellent ingredient with low molecular weight peptides (size < 5000 Da) for fish nutrition

details fish hydrolysates used in aquaculture commercially, their claimed bioactivities and manufacturers.

6. FPHs as Biostimulants

Several groups throughout history including the Incas and Norwegians have used fish by-products as fertilisers. When fishery by-products are not suitable for use as fishmeal, they can be converted to biostimulants by applying enzymes, chemicals, or endogenous enzymes using hydrolysis methods/autolysis, as reviewed recently by [196]. Nowadays, the use of FPHs as biostimulants in Europe must comply with European Regulation 2021/1165 that prohibits the application of fish viscera, for example, on the edible part of plants produced using organic farm practices. Reports state that there are approximately 154 commercial fish fertilisers and biostimulants that exist as pellets, liquids, emulsions or powder products [197].

Biostimulants play a crucial role in modern day agricultural practices and can be defined as “any substance or microorganism, when applied to plants, that can improve nutrition efficiency, abiotic stress tolerance, and crop quality traits, regardless of its nutrient content” [198]. Protein hydrolysates are a primary category of biostimulants and can be made from plant or animal materials. The biostimulants effect of FPHs are due to the amino acids and peptides that can impart “hormone-like” activities to the plant. They can also enhance tolerance to abiotic stress and can stimulate antioxidant and osmoregulation in plants but a lot concerning the mode of action of FPH as biostimulants is still unknown. Figure 1 details the different modes of action of biostimulants and FPHs. Madende and colleagues also recently reviewed this topic [199].

6.1. Mechanisms of Action of FPH Biostimulants

The composition of FPHs impact the biostimulant impact on plants as well as where the FPH is applied (i.e., either soil or to leaves or roots). Results that follow application of biostimulants to plants are species and product specific [200]. Leaf permeability and penetration of the biostimulant are important factors that determine the efficacy of biostimulants. It is known, for example, that foliar application of FPHs increases amino acid and peptide availability by the plant as this form of application reduces competition with soil microbes for the amino acids and peptides present in biostimulants products.

Amino-acid-based biostimulants from FPHs have shown promising benefits and this market is likely to grow in the coming years. The synthesis of amino acids by plants requires a lot of energy consumption and application of amino-acids in FPHs via foliar application allows the plant to save energy by regulation of nitrogen in roots that increases the speed of production during transplantation or climate stress conditions like drought. Amino acids also bind to or chelate metal ions and use of micronutrients with amino acids accelerates absorption of micronutrients and their transport within the plant which results in increased growth. Nitrogen-containing compounds have a positive effect on photosynthetic activity in plants and proline and glutamic acid are known to play a positive role in this activity which can result in greater yields of fruits from plants. Glutamic acid is abundant in FPHs.

6.2. Modes of Action of FPH as Biostimulants

FPH contain a range of amino acids and of these, glutamic acid is a primary component. A myriad of studies have reported that a supply of isolated or combined amino acids is beneficial in the vegetative phase of different plants like beet, lettuce, and tomatoes [196]. Histidine and ornithine are normally absent from FPHs but they can also contain phytohormones, carbohydrates, and minerals. FPHs usually do not contain phenolics like seaweed or plant-based biostimulants. Peptides may have hormonal activities and can help to modulate biochemical processes in plants via biotic and abiotic stimulus [201]. Examples of peptides used as biostimulants include polypeptide families like the systemins and the peptide NOD40, which can promote root nodulation in plants including rice and soybean) [202]. The mechanism of action of FPHs is due to amino acids and peptides mimicking the action of natural peptides with hormone activities in the plants. Fat free amino acids like aspartic acid, hydroxyproline, threonine, serine, glutamic acid, proline, glycine, alanine, methionine, isoleucine, leucine, tyrosine, melatonin, organic matter, short-chain peptides, and proteins are considered the active, biostimulants agents in FPHs. These compounds can improve the utilisation of nutrients by the plants and induce morphological changes in root architecture [203]. Other bioactivities include anti-drought effects and stimulation of beneficial microbes as well as increased antioxidant benefits. These benefits improve the biology of the plant and improve root growth and development, flowering and improved fruit setting, and reduced fruit drop [203]. The biostimulant market in the EU is valued at USD 2.91 billion.

Table 5. Commercial examples of biostimulants including those made from animal protein.

Products	Manufacturer	Origin	Bioactive	Application Method	Plant Trials	Bioactivity
CBio Biostimulant	C Fish (Charlie Vial) (Dunkineely, Co. Donegal, Ireland)	White fish/mixed fish composition autolysates and hydrolysates	Peptides, amino acids	Foliar, pre-planting, irrigation	Fruits and vegetables	Enhances plant resistance to biotic (insect, disease) and abiotic (heat, drought) stresses.
Radifarm	Valagro (Atessa, Chieti, Italy)	Commercial formulation	Amino acids, peptides, saponins, betaines, polysaccharides, vitamins, microelements	Irrigation, soil drench, foliar application	Fruits and vegetables	Stimulates extensive root architecture by accelerating lateral and adventitious root elongation.
Megafol	Syngenta Biologicals (Basel, Switzerland)	Commercial formulation	Amino acids, betaines, proteins, vitamins, auxin, gibberellin	Irrigation, soil drench, foliar application	Fruits and vegetables	Supports balanced vegetative growth, boosts overall productivity, and strengthens resilience to environmental stresses such as frost, root asphyxia, weeding, and hail.
BioRoot	DASA’s elfer® (Menàrguens, Lleida, Spain)	Plant and mineral derived organic humates, soybean meal	Plant derived protein hydrolysate	Irrigation, foliar, soil drench	Irrigation, foliar, soil drench of fruits and vegetables	Improves rooting efficiency while increasing chlorophyll and protein content in plant tissues.
Ergonfill	K—Adriatica (Loreo, Italy)	Animal derived protein hydrolysate	Animal protein hydrolysates, cysteine, folic acid, keratin derivatives	Foliar, pre-planting, irrigation	Fruits and vegetables	Promotes synthesis of indole-3-acetic acid (IAA) and chlorophyll, enhancing nutrient translocation and chelation of macro and micronutrients.

details commercial examples of biostimulants available currently, including those derived from animal protein sources.

The composition of FPHs impact the biostimulant impact on plants as well as where the FPH is applied (i.e., either soil or to leaves or roots). Results that follow application of biostimulants to plants are species and product specific [204]. Leaf permeability and penetration of the biostimulant are important factors that determine the efficacy of biostimulants. It is known, for example, that foliar application of FPHs increases amino acid and peptide availability by the plant as this form of application reduces competition with soil microbes for the amino acids and peptides present in biostimulants products.

Amino-acid-based biostimulants from FPHs have shown promising benefits and this market is likely to grow in the coming years. The synthesis of amino acids by plants requires a lot of energy consumption and application of amino-acids in FPHs via foliar application allows the plant to save energy by regulation of nitrogen in roots that increases the speed of production during transplantation or climate stress conditions like drought. Amino acids also bind to or chelate metal ions and use of micronutrients with amino acids accelerates absorption of micronutrients and their transport within the plant, which results in increased growth. Nitrogen containing compounds have a positive effect on photosynthetic activity in plants and proline and glutamic acid are known to play a positive role in this activity which can result in greater yields of fruits from plants. Glutamic acid is abundant in FPHs [205].

6.3. Product Development

Recently, Venslauskas and colleagues looked at the economic feasibility of using fish viscera as biostimulants [160]. This review suggests that producing biostimulants using a biorefinery approach where fish oil can also be recovered can make the process economically feasible. Key inhibiting factors in terms of costs include enzyme costs and energy consumption costs. Liquid production can reduce costs significantly compared to a dry product, but the shelf life of dry products is greater. Conversion of fish-products to hydrolysates for biostimulant use is also feasible using ensiling or autolysis with endogenous enzymes; however, reproducibility of the end product can vary significantly if the hydrolysis process is not carefully controlled with enzymes or acid. The production strategies of FPHs were recently described by [206].

6.4. Current Research Gaps

FPHs are used today as supplementary products to improve plant growth and survival and increase crop yields. However, there are still several research gaps that exist concerning their mechanism of action on plants and effectiveness. It is necessary to define the underlying genetic, molecular, and physiological mechanisms that contribute to observed field trial results. This would likely increase use of FPH biostimulant products in agriculture. Further, according to Ruzzi et al. figuring out the best combination of “biostimulant × plant species × environment interaction × agricultural practices” is essential to select optimal combinations for improved yields, quantity, and quality of products and optimising the application process in terms of time and rate are necessary to improve the impacts of FPHs as biostimulants [207].

7. Conclusions

The utilisation of fish protein hydrolysates (FPHs) derived from underutilised species and fish processing by-products represents a strategic intersection of sustainability, innovation, and market expansion. As highlighted throughout this review, FPHs are proving to be highly versatile bioactive ingredients with broad applications across human nutrition, companion animal wellness, aquaculture, and agriculture. Their functional value lies primarily in the presence of bioactive peptides and amino acids, which offer targeted health benefits, performance enhancement, and disease resistance across species and systems. In agriculture, their role as biostimulants aligns with the global movement towards reduced reliance on chemical fertilisers and pesticides, while in food and feed industries, they offer both nutritional and sensory improvements.

Advancements in hydrolysate production technologies, especially through enzymatic methods and data-driven approaches like in silico modelling, are enhancing both the efficiency and specificity of FPHs. These tools, once considered auxiliary, are now central to optimising yield, reducing costs, and tailoring bioactivity to meet specific market demands. Moreover, integrated analytical techniques such as plant phenomics and metabolomics are beginning to clarify the mechanisms through which FPHs exert their beneficial effects, especially in agricultural applications.

The growing recognition of FPHs as preventive and functional dietary components across human and animal health sectors points to their expanding commercial and therapeutic significance. As such, continued investment in research and refinement of production methodologies will be key to unlocking their full potential. However, to fully realise these benefits, further work is needed to standardise production, enhance bioactivity targeting, and navigate regulatory and consumer acceptance hurdles—particularly in regions with stringent guidelines such as the European Union.

Overall, the findings of this review underscore the potential of FPHs for sustainable food production, both crop and animal based, as well as promotion of animal and human health, and collates the potential market value that can be garnered from the described scientific studies related to these benefits.